In 2002, the mobile phone service of the 3G system, which is called the third generation in Japan, started. At first, small-size packets were transmitted and received for voice calls and mail transmission. However, with the introduction of high speed downlink packet access (HSDPA), it became possible to transmit and receive larger-size packets for downloading of music files or streaming of video. With such an increase of packet capacities, the service of long term evolution (LTE) in which orthogonal frequency division multiple access (OFDMA) is used on the downlink also started for the expansion on the side of the wireless network. In addition, the 4G service is scheduled to be started in around 2015. Accordingly, up to 1 Gbps (bit per second) is achieved in a semi-fixed environment and up to 100 Mbps is achieved even in a mobile environment.
With such increase in network traffic, it is desirable that a small base station that is inexpensive and easy to install is provided, thereby preventing the concentration of traffic. Various techniques are developed for such a small cell.
As one example, Patent Literature 1 discloses the technique for selecting a device that operates as an access point for a mobile station based on the quality obtained by measuring a wireless signal transmitted from one or more terminal devices.